fix(auth): allow compatible provider API tokens (#34)

Remove the hard `sk-` prefix validation from API key input so users can configure DeepSeek-compatible third-party provider tokens with custom base URLs.

Keep empty input validation and trimmed storage behavior, update the API key prompt copy to clarify that official DeepSeek keys usually start with `sk-`, and relax README setup wording accordingly.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Vizards <13443193+Vizards@users.noreply.github.com>

Author: Copilot

README.md

@@ -59,13 +59,13 @@ Pure VS Code API + Node.js built-ins. No Python, no Docker, no local proxy serve
 
 - VS Code 1.116 or later. This extension relies on non-public Copilot Chat APIs that may break on newer VS Code versions — [report an issue](https://github.com/Vizards/deepseek-v4-for-copilot/issues) if you hit one.
 - GitHub Copilot subscription (Free / Pro / Enterprise — the free tier works)
-- DeepSeek API key from [platform.deepseek.com](https://platform.deepseek.com)
+- DeepSeek API key from [platform.deepseek.com](https://platform.deepseek.com), or a compatible provider token when using a custom `deepseek-copilot.baseUrl`
 
 ### Usage
 
 1. Install from the VS Code Marketplace
 2. Run **DeepSeek: Set API Key** from the Command Palette (`Cmd+Shift+P`)
-3. Paste your key (starts with `sk-`)
+3. Paste your key or compatible provider token (official DeepSeek keys usually start with `sk-`)
 4. Open Copilot Chat, click the model picker, pick **DeepSeek V4 Pro** or **DeepSeek V4 Flash**
 5. That's it — chat away
 

src/auth.ts

@@ -66,9 +66,6 @@ export class AuthManager {
 				if (!value?.trim()) {
 					return t('auth.emptyValidation');
 				}
-				if (!value.startsWith('sk-')) {
-					return t('auth.prefixValidation');
-				}
 				return undefined;
 			},
 		});

src/i18n.ts

@@ -24,10 +24,9 @@ const zh: Translations = {
 
 	// API Key
 	'auth.apiKeyRequiredDetail': '请先配置 API Key',
-	'auth.prompt': '请输入 DeepSeek API Key',
-	'auth.placeholder': 'sk-...',
+	'auth.prompt': '请输入 DeepSeek API Key 或兼容服务令牌。官方 DeepSeek Key 通常以 "sk-" 开头。',
+	'auth.placeholder': 'sk-... 或服务商令牌',
 	'auth.emptyValidation': 'API Key 不能为空',
-	'auth.prefixValidation': 'API Key 应以 "sk-" 开头',
 	'auth.saved': 'API Key 已安全保存。',
 	'auth.removed': 'API Key 已移除。',
 	'auth.notConfigured': 'API Key 未配置，请在命令面板运行 "DeepSeek: 设置 API Key"。',
@@ -64,10 +63,10 @@ const en: Translations = {
 
 	// API Key
 	'auth.apiKeyRequiredDetail': 'Please run DeepSeek: Set API Key to configure.',
-	'auth.prompt': 'Enter your DeepSeek API key',
-	'auth.placeholder': 'sk-...',
+	'auth.prompt':
+		'Enter your DeepSeek API key or compatible provider token. Official DeepSeek keys usually start with "sk-".',
+	'auth.placeholder': 'sk-... or provider token',
 	'auth.emptyValidation': 'API key cannot be empty',
-	'auth.prefixValidation': 'API key should start with "sk-"',
 	'auth.saved': 'DeepSeek API key saved.',
 	'auth.removed': 'DeepSeek API key removed.',
 	'auth.notConfigured':